Greetings...Fluval 406: Canister full, filter media mostly replaced, hoses flushed through, no kinks or excessive tubing. On start up, some intermittent air bubbles and detritus are discharged from the 'out' tube but no apparent flow. and not even sure intake is happening. Motor noisy, but there is a satisfying 'whoosh' when tilted but this not sustained. What have I done wrong?